A multi-methodological approach aimed at deepening the understanding of the relationships between surface water and groundwater through measurements in the hyporheic zone: Case study of Muravera (Southeast Sardinia, Italy).

A multi-methodological approach aimed at deepening the understanding of the relationships between surface water and groundwater through measurements in the hyporheic zone. Case study of Muravera (Southeast Sardinia - Italy) Fabrizio Antonio Piscedda*, Richard Wanty**, Claudio Arras*, Maria Chiara Porru*, Francesca Podda*, Elodia Musu*, Riccardo Biddau*, Stefania Da Pelo* * Department of chemical and Geological Science – University of Cagliari – Campus of Monserrato, Building A ** Colorado School of Mines, Department of Geology and Geological Engineering The volume of riverbed sediments where water can move from streams to aquifers and vice-versa is known as hyporheic zone. Here, water movements can occur through different timeframes ranging from days to months. Within this volume, variations of chemical-physical properties and head gradients can be observed between surface waters and ground waters. In this study we investigate interexchange relationships between surface water (SW) and ground waters (GW) within the hyporheic zone in the coastal aquifer of Muravera (SE Sardinia, Italy), which suffer under ongoing seawater intrusion phenomena. The methodological approach includes monitoring activities along the Flumendosa river and a hydrogeochemical tracing in a channel where treated wastewater is discharged. Mini-piezometers of 100 and 200 cm in length are used to observe the relationships between the SW and GW levels at different depths within the riverbed area, moving from the upstream part of the plain toward the sea; moreover, a 5 mini-piezometers transect, orthogonal to the SW flow direction, is also performed at the groundwater resurgence area. Temperature, specific conductivity, Eh, and pH data are also measured and samples collected to perform chemical analyses. Secondly, a hydrogeochemical tracing with NaCl was carried out in the treated wastewater discharge channel to assess potential leakage from this SW source to the aquifer. Samples from nearby wells are also collected to assess the presence of gadolinium in groundwater and, eventually, to evaluate it for a possible use as a tracer. This study provides valuable insights into the dynamics and relationships between surface water and groundwater by studying the hyporheic zone in the Flumendosa River basin. Therefore, it could be an additional contribution to the enhancement of knowledge regarding the interexchange dynamics between SW and GW in the lower valley of the Flumendosa.